What it is

The KFGS is Kyowa's general-purpose foil strain gage, supplied here with the lead-wire cable already connected. Gages connected with lead wires provide increases in speed and the labor saving required for adhesion, so the wiring is done before the gage reaches the installation. The gage itself uses a polyimide resin base approximately 14 µm (0.00055 in) thick and offers superior flexibility, with excellent humidity resistance for measuring indoors and in the field.

• Gage factor approximately 2.1
• Gage resistance 60 Ω, 120 Ω, 350 Ω, 500 Ω, or 1000 Ω
• Gage lengths from 0.2 mm (0.008 in) to 30 mm (1.181 in)
• Uniaxial base sizes from 3.9 × 1.4 mm (0.154 × 0.055 in) to 37 × 5.2 mm (1.457 × 0.205 in)
• Uniaxial, biaxial, triaxial, quadriaxial, and five-element patterns
• Operating temperature −196 to 150 °C (−321 to 302 °F) depending on adhesive
• Self-temperature-compensation range 10 to 100 °C (50 to 212 °F)
• Lead-wire cable lengths 15 cm to 5 m (5.9 in to 16.4 ft)
• RoHS compliant

What it measures

The KFGS is available in a variety of gage lengths and patterns for use in a wide range of applications:

• General stress measurement on metal under a general environment
• Surface strain on concrete and mortar with small aggregate
• General stress measurement on wood and lumber
• Residual stress by the cutting method — T-F7 gage-terminal patterns
• Residual stress by the boring method — D28 triaxial plane pattern
• Concentrated stress and stress distribution at 8 to 12 mm intervals — D9, D19, and D39 five-element patterns
• Torque — D2 and D31 biaxial plane patterns, or C15 and C16 shear patterns used in combination
• Poisson's ratio and stress analysis — D16 biaxial and D17 triaxial stacked rosettes
• Sensing elements for transducers — high-resistance 350 Ω, 500 Ω, and 1000 Ω uniaxial C1 patterns

Base, compensation, and endurance

Polyimide base, 14 µm. The polyimide resin base is approximately 14 µm (0.00055 in) thick and offers superior flexibility, with excellent humidity resistance for use when measuring indoors and in the field.

Self-temperature compensation matched to the substrate. Each gage carries a linear expansion coefficient code selected to match the test material — 11 for common steel (11.7), 16 for SUS304 stainless steel (16.2), 23 for A2014-T4 aluminum alloy (23.4), 27 for magnesium alloy (27.0), and 5 for lumber on selected uniaxial patterns. Self-temperature compensation covers 10 to 100 °C (50 to 212 °F), and the base color identifies the applicable linear expansion coefficient.

Strain limit and fatigue life. The strain limit is approximately 5.0% at normal temperature, with a fatigue life of 1.2 × 10⁷ cycles at a ±1500 µm/m strain level.

Lead-wire cables

The lead-wire cable is selected to match the measurement environment and temperature, and it is the cable that sets the temperature range of the wired assembly:

• 2 or 3 polyester-coated copper wires — −196 to 150 °C (−321 to 302 °F), in 15 cm, 30 cm, and 1 m (5.9 in, 11.8 in, 3.3 ft) lengths. Twisted for lengths of 50 cm (19.7 in) and above, with exceptions.
• Vinyl-coated flat 2-wire and 3-wire cables — −10 to 80 °C (14 to 176 °F), in 15 cm, 30 cm, 1 m, 3 m, and 5 m (5.9 in, 11.8 in, 3.3 ft, 9.8 ft, 16.4 ft) lengths.
• Mid-temperature 2-wire and 3-wire cables — −100 to 150 °C (−148 to 302 °F), in the same five lengths. The wire section of the R-type is sandwiched or wrapped with glass-cloth tape for insulation and reinforcement.

Cable availability varies by gage pattern, and other lengths are available on request. On biaxial and triaxial gages the conductors are striped for identification: 2-wire cables use red, white, and green for the 0°, 90°, and 45° elements, and 3-wire cables use red, yellow, and blue for the same elements. The D9, D19, and D39 five-element patterns are supplied with 2 polyester-coated copper wires 10 cm (3.9 in) long plus the specified lead-wire cable.

Configuring the right gage and cable

A KFGS order with a pre-attached cable is written as the gage model number, a space, then the lead-wire cable code — for example KFGS-5-120-C1-11 N15C2 for 2 polyester-coated copper wires 15 cm long, or KFGS-5-120-C1-11 L5M2R for a vinyl-coated flat 2-wire cable 5 m long. If no lead-wire cable code is suffixed, the gage is delivered with gage leads only.

• Pattern matches the measurement application.
• Gage length matches the kind of material and the space available.
• Resistance matches the measurement application: 60 Ω for bending compensation, 120 Ω for general-purpose strain measurement, and 350 to 1000 Ω for transducers.
• Linear expansion code matches the test material.
• Cable code matches the measurement environment and temperature.

Combinations of codes are limited, so not every pattern, length, resistance, and cable can be ordered together. Adhesive is ordered separately and sets the operating temperature of the bond. Configure the gage and cable on this page and buy it directly. If you need something the configurator does not cover — a cable length outside the standard range, a combination that isn't offered, adhesive and installation accessories on the same order, or a gage manufactured to your own measurement purpose — contact us.

The KFGS cannot be used in hydrogen environments. After opening, store gages in a dry environment such as a desiccator, and wear protective glasses when bonding to prevent adhesive entering the eyes. Published characteristics are reference values and will vary with operating conditions such as the temperature effect; to increase measurement accuracy, run a pretest on the actual equipment and compensate based on the result.